Electric machines are well known in the art. They usually have a fixed stator and a rotating rotor. Generally, the stator is external and the rotor is rotatably mounted inside the stator, coaxially therewith.
In some electric machines, the stator is internal and the cylindrical rotor is coaxially mounted outside the stator. These machines will be referred herein as internal stator electric machines.
Cooling internal stator machines is a challenge since one cannot rely on the air surrounding the stator as a cooling medium to cool the stator by convection. Indeed, it is well known that heat is mainly generated inside the stator of an electric machine. When the stator is external, fins may be added to the machine casing and the machine may be cooled by convection. However, when the stator is surrounded by the rotor, adequate convection cooling may not take place and other ways must be devised to extract heat from the internal stator.